7/31 [Chien-Ming and Hsun-Chung]

We investigate the reasons for the squeezing level decline on 28th July http://www2.nao.ac.jp/~gw-elog/osl/?r=3305.
Originally we suspected it was caused by poor cleaning of the optics, but today we found out that the phase-matching temperature of OPO is not at the optimal value.

On 7/28 we set OPO T=7.159 kOhm with 25mW green pump and T=7.184 kOhm with 40mW green respectively in order to lock the p-pol at 270MHz.
Today we check that the optimal value of OPO T should be set near 7.107 kOhm to achieve the maximum nonlinear gain.

OPOT=7.107k; 25mW green; BAB Max=1.26V; p-pol=33MHz*5=165MHz.
Without green; BAB=196mV-6mV(Background)=190mV; p-pol=49MHz*5=245MHz.
Therefore the nonlinear gain=6.63 at 25mW pump.

HOM visibility:
LO at AMC: TEM00=5.96v; hom=2.4mV+2.4mV; mode-matching: 99.92%
BAB at AMC: TEM00= 196mV; hom=6.4mV+1.8mV; mode-matching: 95.98%

SHG output power in front of MZ drops to 165.5mW even if the SHG temperature and alignment are optimized (194.9mW on 7/28)

We preset the SR785, however, the parameters are incorrect so the squeezing measurement is weird today.